Grid resolution study of ground water flow and transport

Three-dimensional grids representing a heterogeneous, ground water system are generated at 10 different resolutions in support of a site-scale flow and transport modeling effort. These grids represent hydrostratigraphy near Yucca Mountain, Nevada, consisting of 18 stratigraphic units with contrasting fluid flow and transport properties. The grid generation method allows the stratigraphy to be modeled by numerical grids of different resolution so that comparison studies can be performed to test for grid quality and determine the resolution required to resolve geologic structure and physical processes such as fluid flow and solute transport. The process of generating numerical grids with appropriate property distributions from geologic conceptual models is automated, thus making the entire process easy to implement with fewer user-induced errors. The series of grids of various resolutions are used to assess the level at which increasing resolution no longer influences the flow and solute transport results. Grid resolution is found to be a critical issue for ground water flow and solute transport. The resolution required in a particular instance is a function of the feature size of the model, the intrinsic properties of materials, the specific physics of the problem, and boundary conditions. The asymptotic nature of results related to flow and transport indicate that for a hydrologic model of the heterogeneous hydrostratigraphy under Yucca Mountain, a horizontal grid spacing of 600 m and vertical grid spacing of 40 m resolve the hydrostratigraphic model with sufficient precision to accurately model the hypothetical flow and solute transport to within 5% of the value that would be obtained with much higher resolution.     

东北太平洋锋面系统的结构

１９８０年１１月１７日一条锋面系统经过风暴输送和响应试验区，由船舶无线电探空测风仪，地面和雷达资料揭示出此东北太平洋风暴表现为三个组成部分；它连接地面和５００ｈＰａ槽具有显著的地面风向转变，汇合和水平风切变，没有地面温度的变化；一条中对流层的冷性下滑锋和一条比其它部分向前移动更迅速的上层湿度锋，上层湿度锋的特征是横越大片云区部边缘的湿度梯度，它随着５００ｈＰａ或以上的风移动，由于海洋边层水平温度的     

Radar determination of the spatial structure of hydraulic conductivity

Spatial variability of hydraulic conductivity exerts a predominant control on the flow of fluid through porous media. Heterogeneities influence advective pathways, hydrodynamic dispersion, and density-dependent dispersion; they are, therefore, a key concern for studies of ground water resource development, contaminant transport, and reservoir engineering. Ground-penetrating radar contributes to the remote, geophysical characterization of the macroscale variability of natural porous media. On a controlled excavation of a glacial-fluvial sand and gravel deposit in the Fanshawe Delta area (Ontario, Canada), the hydraulic conductivity field of a 45 x 3 m vertical exposure was characterized using constant-head permeameter measurements performed on undisturbed horizontal sediment cores. Ground-penetrating radar data were collected along the excavation face in the form of both reflection and common midpoint surveys. Comparison of geostatistical analyses of the permeameter measurements and the radar data suggests thatthe horizontal correlation structure of radar stack velocity can be used to directly infer the horizontal correlation structure of hydraulic conductivity. The averaging nature of the common midpoint survey is manifest in the vertical correlation structure of stack velocity, making it less useful. Radar reflection data do not exhibit a spatial structure similar to that of hydraulic conductivity possibly because reflections are a result of material property contrasts rather than the material properties themselves.     

地震活动时序谱的涨落统计特征与地震活跃期

为寻求地震活动演化的统计判据，本文采用多项式拟合法展示地震时序谱之涨落谱，以分维函数法判断最小邻间距（NNS）分布的Poisson性，然后采用MKS无参量法判别涨落谱之统计稳定性，确定NNS分布的转变区，具体研讨了四川、云南若干震区地震活动时序谱的涨落统计分布，发现地震活跃期到来时NNS分布表现出非Poisson化的特征。进一步通过改变和调节时序数据样本集之震级下限，并逐段前推进行统计计算的方式进一步验证结果的可靠性，客观地确定了这些震区地震活动时序涨落谱统计特征的转变期，使根据该统计法判断地震活跃期的方法论渐趋完善。     

汶川地震后的几点思考

本文认真思考了汶川地震对防震减灾各环节的影响,主要观点有:(1)地震预报很难,但不能不搞。(2)搞好建筑物的抗震设防、避让活断层与山地灾害隐患,或适当治理山地灾害隐患是震前防御减灾的有效途径。(3)汶川地震的紧急救援绩效卓著,但还有提升潜力。     

科学化、实用化是地震预报事业发展的要求

预报总是在机理不完全清楚,或者虽然机理已基本清楚,但受多种复杂因素影响,其结果带有不确定性的领域里才显得重要。例如,现在人类对于日蚀、月蚀的机理已了解得很清楚,可以根据太阳、地球和月球相互之间的作用和相对的运动精确地预测日蚀和月蚀出现的时间,以及可以观测到的地区。这样的预测工作只需由某个天文台计算在天文年